Many integrated circuit applications require a pulse width modulated (PWM) signal. FIG. 1A illustrates a conventional circuit 100 for generating a PWM signal from a ramp voltage reference and an input signal. The widths of respective pulses in the PWM signal are modulated based on the input signal. The PWM signal has a carrier frequency “fref” that is the same frequency as the ramp voltage reference. The duty cycle of each period of the PWM signal depends upon the relative magnitudes of the ramped reference signal and the input signal. Thus, the duty cycle of the PWM signal contains information about the magnitude of the input signal.
FIG. 1B illustrates a conventional circuit 150 for generating a ramped reference voltage, which may be used to create the PWM signal having the same frequency “fref” as the ramped reference voltage signal. The ramped voltage circuit 150 functions by charging the capacitor Cref with the bias current Ibias until the capacitor Cref is at the reference voltage VDc—ref. During this period, the output voltage ramps up. When the output voltage reaches the reference voltage, the capacitor Cref rapidly discharges to create the saw-tooth waveform of the output ramped reference voltage.